The invention relates to aspiration devices for use with immunoassays of the type which employ immunobeads or immunoballs. More particularly, the invention relates to devices for aspirating fluids from test tubes, microtiter wells, or other immunoassay incubation vessels which contain immunobeads or immunoballs and which enhance the completion of the aspiration process by picking up the immunobead or immunoball.
For a conventional immunoassay, multiple liquids must be dispensed and aspirated from an immunoassay reaction vessel. The automation of immunoassays requires the mechanization of such multiple liquid dispensing and aspiration steps. The reliability of the immunoassay is dependent upon the accuracy of the dispensing steps and the completeness of the aspiration steps. Incomplete aspiration may result in the carry over of unreacted or unbound species from one step in the assay to the next. Such carry over may necessitate further wash steps or may result in the introduction of inaccuracy.
Immunoassays which employ immunobeads or immunoballs can be particularly difficult to aspirate completely. It has been found that lifting the immunobead or immunoball during the aspiration procedure reduces the amount of carry over liquid which remains between the immunobead and the bottom of the immunoassay incubation vessel. Aspirators having an inverted bowl may be employed for lifting the immunobead during such aspiration procedures. If a vacuum is pulled from this inverted bowl, the inverted bowl can lift the immunobead. To facilitate the capture of the immunobead, the inverted bowl may be given a shape which is complementary to the shape of the immunobead, i.e. the immunobead may fit snugly into the inverted bowl. To prevent the clogging of the vacuum port by the immunobead, longitudinal channels may be formed within the inverted bowl extending from the vacuum port to the rim. Aspirated liquids may travel within these channels to the vacuum source. The aspiration of liquids is also facilitated if the rim of the inverted bowl extends proximally to the side walls of the immunoassay incubation vessel. Accordingly, it has been found that liquids may be aspirated from the bottom of the vessel by lifting and capturing the immunobead and by then drawing the vacuum proximally to the wall of the vessel through these channels.
Unfortunately, the capture of the immunobead by the inverted bowl can cause liquid to be trapped within the contact area between the immunobead and the inverted bowl. Such trapped liquid can cause incomplete aspiration and liquid carry over.
What is needed is an aspiration device for use with immunobeads and immunoballs which can reduce the amount liquid carry over between aspiration steps.